Pneumatic tire having tread with three elastomers

ABSTRACT

The present invention is directed to a pneumatic tire comprising a vulcanizable rubber composition, the vulcanization rubber composition comprising: 1) 100 parts by weight of elastomer consisting of 25 to 35 phr of a styrene-butadiene rubber, 25 to 35 phr of a polybutadiene, and 35 to 45 phr of a natural rubber or synthetic polyisoprene, wherein the styrene-butadiene rubber is a functionalized solution polymerized styrene-butadiene elastomer having a glass transition temperature Tg(A) ranging from −30 to −10° C. and having at least one functional group; the natural rubber or synthetic polyisoprene has a Tg(B) ranging from −60 to −70° C.; and the polybutadiene is a cis 1,4 polybutadiene having a Tg(C) ranging from −110 to −90° C., wherein Tg(A)−Tg(B)≥25° C., and Tg(B)−Tg(C)≥25° C.; 2) 60 to 80 phr of a prehydrophobated silica; 3) 1 to 10 phr of carbon black; 4) 1 to 3 phr of rubber processing oil; and 5) 5 to 25 phr of at least one hydrocarbon resin having a Tg≥20° C., wherein the weight ratio of hydrocarbon resin to rubber processing oil is greater than 8.

BACKGROUND OF THE INVENTION

It is highly desirable for tires to have good wet skid resistance, lowrolling resistance, and good wear characteristics. It has traditionallybeen very difficult to improve a tire's wear characteristics withoutsacrificing its wet skid resistance and traction characteristics. Theseproperties depend, to a great extent, on the dynamic viscoelasticproperties of the rubbers utilized in making the tire.

In order to reduce the rolling resistance and to improve the treadwearcharacteristics of tires, rubbers having a low hysteresis havetraditionally been utilized in making tire tread rubber compounds. Onthe other hand, in order to increase the wet skid resistance of a tire,rubbers which undergo a large energy loss have generally been utilizedin the tire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instance,various mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubbery material for automobile tire treads.However, improvements in rolling resistance often occur in tandem with areduction in wet traction, and vice versa. There is a continuing need,therefore, to develop tread having both good rolling resistance and wettraction.

SUMMARY OF THE INVENTION

The present invention is directed to a pneumatic tire comprising avulcanizable rubber composition, the vulcanization rubber compositioncomprising:

1) 100 parts by weight of elastomer consisting of 25 to 35 phr of astyrene-butadiene rubber, 25 to 35 phr of a polybutadiene, and 35 to 45phr of a natural rubber or synthetic polyisoprene,

wherein the styrene-butadiene rubber is a functionalized solutionpolymerized styrene-butadiene elastomer having a glass transitiontemperature Tg(A) ranging from −30 to −10° C. and having at least onefunctional group; the natural rubber or synthetic polyisoprene has aTg(B) ranging from −65 to −70° C.; and the polybutadiene is a cis 1,4polybutadiene having a Tg(C) ranging from −110 to −90° C.,

wherein Tg(A)−Tg(B)≥25° C., and Tg(B)−Tg(C)≥25° C.;

2) 60 to 80 phr of a prehydrophobated silica;

3) 1 to 10 phr of carbon black;

4) 1 to 3 phr of rubber processing oil; and

5) 5 to 25 phr of at least one hydrocarbon resin having a Tg≥20° C.;wherein the weight ratio of hydrocarbon resin to rubber processing oilis greater than 8.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a pneumatic tire comprising a vulcanizable rubbercomposition, the vulcanization rubber composition comprising:

1) 100 parts by weight of elastomer consisting of 25 to 35 phr of astyrene-butadiene rubber, 25 to 35 phr of a polybutadiene, and 35 to 45phr of a natural rubber or synthetic polyisoprene,

wherein the styrene-butadiene rubber is a functionalized solutionpolymerized styrene-butadiene elastomer having a glass transitiontemperature Tg(A) ranging from −30 to −10° C. and having at least onefunctional group; the natural rubber or synthetic polyisoprene has aTg(B) ranging from −60 to −70° C.; and the polybutadiene is a cis 1,4polybutadiene having a Tg(C) ranging from −110 to −90° C.,

wherein Tg(A)−Tg(B)≥25° C., and Tg(B)−Tg(C)≥25° C.;

2) 60 to 80 phr of a prehydrophobated silica;

3) 1 to 10 phr of carbon black;

4) 1 to 3 phr of rubber processing oil; and

5) 5 to 25 phr of at least one hydrocarbon resin having a Tg≥20° C.;wherein the weight ratio of hydrocarbon resin to rubber processing oilis greater than 8.

In one embodiment, the rubber composition comprises 100 parts by weightof elastomer consisting of 25 to 35 phr of a styrene-butadiene rubber,25 to 35 phr of a polybutadiene, and 35 to 45 phr of a natural rubber orsynthetic polyisoprene.

In one embodiment, at styrene-butadiene rubber is functionalized with analkoxysilane group and at least one group selected from sulfurcontaining functional group and primary amino functional groups.

In one embodiment, the rubber composition includes from 25 to 35 phr ofa styrene-butadiene rubber functionalized with an alkoxysilane group anda functional group selected from sulfur containing functional groups andamino functional groups. Suitable sulfur containing groups includethiol, thioether, thioester, sulfide, or sulfanyl group. Suitable aminofunctional groups include primary, secondary, and tertiary amino groups.Additional examples of rubbers which may be used include solutionpolymerized styrene-butadiene functionalized with groups such as alkoxyincluding monoalkoxy, dialkoxy, and trialkoxy, silyl, thiols, thioester,thioether, sulfanyl, mercapto, sulfide, and combinations thereof. Suchfunctionalized solution polymerized polymers may be functionalized atthe polymer chain ends for example via functional initiators orterminators, or within the polymer chains for example via functionalmonomers, or a combination of in-chain and end-of-chainfunctionalization. Specific examples of suitable functional solutionpolymerized polymers include those described in U.S. Pat. Nos. 8,217,103and 8,569,409 having alkoxysilyl and sulfide (i.e. thioether)functionality. Such thiol functionality includes thiol or sulfanylfunctionality arising from cleavage of sulfur containing groups duringcompound processing, such as for example from thioesters and thioethers.

In one embodiment, the styrene-butadiene rubber is obtained bycopolymerizing styrene and butadiene, and characterized in that thestyrene-butadiene rubber has a thiol group and an alkoxysilyl groupwhich are bonded to the polymer chain. In one embodiment, thealkoxysilyl group is an ethoxysilyl group.

The thiol group may be bonded to any of a polymerization initiatingterminal, a polymerization terminating terminal, a main chain of thestyrene-butadiene rubber and a side chain, as long as it is bonded tothe styrene-butadiene rubber chain. However, the thiol group ispreferably introduced to the polymerization initiating terminal or thepolymerization terminating terminal, in that the disappearance of energyat a polymer terminal is inhibited to improve hysteresis losscharacteristics. The thiol group may further exist as a blocked thiol(also known as blocked mercapto group) having a protective functionalgroup attached to the sulfur atom such as in a thioester or thioether,which is then cleaved to expose the thiol sulfur during rubber mixing.

Further, the content of the alkoxysilyl group bonded to the polymerchain of the (co)polymer rubber is preferably from 0.5 to 200 mmol/kg of(styrene-butadiene rubber. The content is more preferably from 1 to 100mmol/kg of styrene-butadiene rubber, and particularly preferably from 2to 50 mmol/kg of styrene-butadiene rubber.

The alkoxysilyl group may be bonded to any of the polymerizationinitiating terminal, the polymerization terminating terminal, the mainchain of the (co)polymer and the side chain, as long as it is bonded tothe (co)polymer chain. However, the alkoxysilyl group is preferablyintroduced to the polymerization initiating terminal or thepolymerization terminating terminal, in that the disappearance of energyis inhibited from the (co)polymer terminal to be able to improvehysteresis loss characteristics.

The styrene-butadiene rubber can be produced by polymerizing styrene andbutadiene in a hydrocarbon solvent by anionic polymerization using anorganic alkali metal and/or an organic alkaline earth metal as aninitiator, adding a terminating agent compound having a primary aminogroup protected with a protective group and/or a thiol group protectedwith a protecting group and an alkoxysilyl group to react it with aliving polymer chain terminal at the time when the polymerization hassubstantially completed, and then conducting deblocking, for example, byhydrolysis or other appropriate procedure.

The solution polymerized styrene-butadiene rubber has a glass transitiontemperature in a range from −30° C. to −10° C. A reference to glasstransition temperature, or Tg, of an elastomer or elastomer composition,where referred to herein, represents the glass transition temperature(s)of the respective elastomer or elastomer composition in its uncuredstate or possibly a cured state in a case of an elastomer composition. ATg can be suitably determined as a peak midpoint by a differentialscanning calorimeter (DSC) at a temperature rate of increase of 10° C.per minute, for example according to ASTM D7426 or equivalent.

Suitable styrene-butadiene rubbers functionalized with an alkoxysilanegroup and a thiol group are available commercially, such as SOL 5360Hfrom Kumho Petrochemical.

Another component of the rubber composition is from about 35 to about 45phr of natural rubber or synthetic cis 1,4-polyisoprene having a Tgranging from −60 to −70° C. Such natural rubber or synthetic cis1,4-polyisoprene are well known to those skilled in the art.

Another component of the rubber composition is from 25 to about 35 phrof cis-1,4 polybutadiene, also known as polybutadiene rubber orpolybutadiene (BR). Suitable polybutadiene rubbers may be prepared, forexample, by organic solution polymerization of 1,3-butadiene usinglithium or neodymium catalysts. The BR may be convenientlycharacterized, for example, by having at least a 90 percent cis1,4-content and a glass transition temperature Tg in a range of from −90to −110° C. Suitable polybutadiene rubbers are available commercially,such as Budene® 1223 from Goodyear and the like.

As noted earlier, the styrene-butadiene rubber is a functionalizedsolution polymerized styrene-butadiene elastomer having a glasstransition temperature referred to herein as Tg(A) which ranges from −30to −10° C.; the natural rubber or synthetic polyisoprene has a Tg(B)ranging from −65 to −70° C.; and the polybutadiene is a cis 1,4polybutadiene having a Tg(C) ranging from −110 to −90° C. Thestyrene-butadiene rubber, natural rubber or synthetic polyisoprene, andpolybutadiene satisfy the relationships Tg(A)−Tg(B)≥25° C., andTg(B)−Tg(C)≥25° C.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition includes from 5 to 25 phr of a hydrocarbon resinhaving a Tg greater than or equal to 20° C. A suitable measurement of Tgfor resins is DSC according to ASTM D6604 or equivalent.

Representative hydrocarbon resins include coumarone-indene-resins,petroleum resins, C5/C9 resins, terpene polymers, alphamethyl styreneresins and mixtures thereof.

Coumarone-indene resins are well known. Various analysis indicate thatsuch resins are largely polyindene; however, typically contain randompolymeric units derived from methyl indene, coumarone, methyl coumarone,styrene and methyl styrene.

Suitable petroleum resins include both aromatic and nonaromatic types.Several types of petroleum resins are available. Some resins have a lowdegree of unsaturation and high aromatic content, whereas some arehighly unsaturated and yet some contain no aromatic structure at all.Differences in the resins are largely due to the olefins in thefeedstock from which the resins are derived. Conventional derivatives insuch resins include dicyclopentadiene, cyclopentadiene, their dimers anddiolefins such as isoprene and piperylene. Copolymers of these monomerwith one another or with aromatic such as styrene and alphamethylstyrene are also included.

In one embodiment the resin is an aromatic modifiedpolydicyclopentadiene.

Terpene polymers are commercially produced from polymerizing a mixtureof alpha or beta pinene in mineral spirits. The resin is usuallysupplied in a variety of melting points ranging from 10° C. to 135° C.

In one embodiment, the resin is derived from styrene andalphamethylstyrene. It is considered that, in one aspect, its glasstransition temperature (Tg) characteristic combined with its molecularweight (Mn) and molecular weight distribution (Mw/Mn) provides asuitable compatibility of the resin in the rubber composition, thedegree of compatibility being directly related to the nature of therubber composition.

The presence of the styrene/alphamethylstyrene resin with a rubber blendwhich contains the presence of the styrene-butadiene elastomer isconsidered herein to be beneficial because of observed viscoelasticproperties of the tread rubber composition such as complex and storagemodulus, loss modulus tan.delta and loss compliance at differenttemperature/frequency/strain as hereinafter generally described.

The properties of complex and storage modulus, loss modulus, tan.deltaand loss compliance are understood to be generally well known to thosehaving skill in such art. They are hereinafter generally described.

The molecular weight distribution of the resin is visualized as a ratioof the resin molecular weight average (Mw) to molecular weight numberaverage (Mn) values and is considered herein to be in a range of about1.5/1 to about 2.5/1 which is considered to be a relatively narrowrange. This is believed to be advantageous because of the selectivecompatibility with the polymer matrix and because of a contemplated useof the tire in wet and dry conditions over a wide temperature range.

The glass transition temperature Tg of the copolymer resin is consideredherein to be in a range of about 20° C. to about 100° C., alternativelyabout 30° C. to about 80° C., depending somewhat upon the intended useof the prepared tire and the nature of the polymer blend for the tiretread. A suitable measurement of TG for resins is DSC according to ASTMD6604 or equivalent.

The styrene/alphamethylstyrene resin is considered herein to be arelatively short chain copolymer of styrene and alphamethylstyrene witha styrene/alphamethylstyrene molar ratio in a range of about 0.40 toabout 1.50. In one aspect, such a resin can be suitably prepared, forexample, by cationic copolymerization of styrene and alphamethylstyrenein a hydrocarbon solvent.

Thus, the contemplated styrene/alphamethylstyrene resin can becharacterized, for example, by its chemical structure, namely, itsstyrene and alphamethylstyrene contents and softening point and also, ifdesired, by its glass transition temperature, molecular weight andmolecular weight distribution.

In one embodiment, the styrene/alphamethylstyrene resin is composed ofabout 40 to about 70 percent units derived from styrene and,correspondingly, about 60 to about 30 percent units derived fromalphamethylstyrene. In one embodiment, the styrene/alphamethylstyreneresin has a softening point according to ASTM No. E-28 in a range ofabout 80° C. to about 145° C.

Suitable styrene/alphamethylstyrene resin is available commercially asResin 2336 from Eastman or Sylvares SA85 from Arizona Chemical.

The rubber composition may also include from 1 to 3 phr of processingoil. Processing oil may be included in the rubber composition asextending oil typically used to extend elastomers. Processing oil mayalso be included in the rubber composition by addition of the oildirectly during rubber compounding. The processing oil used may includeboth extending oil present in the elastomers, and process oil addedduring compounding. Suitable process oils include various oils as areknown in the art, including aromatic, paraffinic, naphthenic, vegetableoils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenicoils. Suitable low PCA oils include those having a polycyclic aromaticcontent of less than 3 percent by weight as determined by the IP346method. Procedures for the IP346 method may be found in Standard Methodsfor Analysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

In the rubber composition, the weight ratio of hydrocarbon resin toprocessing oil is greater than 8.

Also included in the rubber composition is from 60 to 80 phr ofpre-hydrophobated precipitated silica. By pre-hydrophobated, it is meantthat the silica is pretreated, i.e., the pre-hydrophobated precipitatedsilica is hydrophobated prior to its addition to the rubber compositionby treatment with at least one silane. Suitable silanes include but arenot limited to alkylsilanes, alkoxysilanes, organoalkoxysilylpolysulfides and organomercaptoalkoxysilanes.

In an alternative embodiment, the pre-hydrophobated precipitated silicamay be pre-treated with a silica coupling agent comprised of, forexample, an alkoxyorganomercaptoalkoxysilane or combination ofalkoxysilane and organomercaptoalkoxysilane prior to blending thepre-treated silica with the rubber instead of reacting the precipitatedsilica with the silica coupling agent in situ within the rubber. Forexample, see U.S. Pat. No. 7,214,731.

The prehydrophobated precipitated silica may optionally be treated witha silica dispersing aid. Such silica dispersing aids may include glycolssuch as fatty acids, diethylene glycols, polyethylene glycols, fattyacid esters of hydrogenated or non-hydrogenated C₅ or C₆ sugars, andpolyoxyethylene derivatives of fatty acid esters of hydrogenated ornon-hydrogenated C₅ or C₆ sugars.

Exemplary fatty acids include stearic acid, palmitic acid and oleicacid.

Exemplary fatty acid esters of hydrogenated and non-hydrogenated C5 andC6 sugars (e.g., sorbose, mannose, and arabinose) include, but are notlimited to, the sorbitan oleates, such as sorbitan monooleate, dioleate,trioleate and sesquioleate, as well as sorbitan esters of laurate,palmitate and stearate fatty acids. Exemplary polyoxyethylenederivatives of fatty acid esters of hydrogenated and non-hydrogenated C5and C6 sugars include, but are not limited to, polysorbates andpolyoxyethylene sorbitan esters, which are analogous to the fatty acidesters of hydrogenated and non-hydrogenated sugars noted above exceptthat ethylene oxide groups are placed on each of the hydroxyl groups.

The optional silica dispersing aids if used are present in an amountranging from about 0.1% to about 25% by weight based on the weight ofthe silica, with about 0.5% to about 20% by weight being suitable, andabout 1% to about 15% by weight based on the weight of the silica alsobeing suitable.

For various pre-treated precipitated silicas see, for example, U.S. Pat.Nos. 4,704,414, 6,123,762, and 6,573,324.

Suitable pre-hydrophobated silica is available commercially for examplefrom PPG as the Agilon series.

In addition to the pre-hydrophobated silica, the rubber composition mayinclude an untreated, or non-prehydrophated precipitated silica.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc.; silicas available from Solvay, with, for example,designations of Z1165MP, Z165GR and Zeosil Premium 200MP and silicasavailable from Degussa AG with, for example, designations VN2 and VN3,etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 1 to 10 phr. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm3/100 g.

In one embodiment, the rubber composition may optionally contain aconventional sulfur containing organosilicon compound. In oneembodiment, the sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In oneembodiment, the sulfur containing organosilicon compounds are3,3′-bis(triethoxysilylpropyl) disulfide and/or3,3′-bis(triethoxysilylpropyl) tetrasulfide.

The amount of the optional sulfur containing organo silicon compound ina rubber composition will vary depending on the level of other additivesthat are used. Generally speaking, the amount of the compound will rangefrom 0.5 to 20 phr. In one embodiment, the amount will range from 1 to10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarder, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidantsand antiozonants and peptizing agents. As known to those skilled in theart, depending on the intended use of the sulfur vulcanizable andsulfur-vulcanized material (rubbers), the additives mentioned above areselected and commonly used in conventional amounts. Representativeexamples of sulfur donors include elemental sulfur (free sulfur), anamine disulfide, polymeric polysulfide and sulfur olefin adducts. In oneembodiment, the sulfur-vulcanizing agent is elemental sulfur. Thesulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8phr, alternatively with a range of from 1.5 to 6 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

In one embodiment, the rubber compositions may include from 1 to 10 phras a vulcanization modifier an α,ω-bis(N,N′-dihydrocarbylthiocarbamamoyldithio)alkane. Suitable α,ω-bis(N,N′-dihydrocarbylthiocarbamamoyldithio)alkanes include1,2-bis(N,N′-dibenzylthiocarbamoyl-dithio)ethane;1,3-bis(N,N′-dibenzylthiocarbamoyldithio)propane;1,4-bis(N,N′-dibenzylth-iocarbamoyldithio)butane;1,5-bis(N,N′-dibenzylthiocarbamoyldithio)pentane;1,6-bis(N,N′-dibenzylthiocarbamoyldithio)hexane;1,7-bis(N,N′-dibenzylthiocarbamoyldithio)heptane;1,8-bis(N,N′-dibenzylthiocarbamoyldithio)octane;1,9-bis(N,N′-dibenzylthiocarbamoyldithio)nonane; and1,10-bis(N,N′-dibenzylthiocarbamoyldithio)decane. In one embodiment, thevulcanization modifier is1,6-bis(N,N′-dibenzylthiocarbamoyldithio)hexane available as Vulcurenfrom Bayer.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 120° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about80° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

Example

In this example, rubber compositions according to the invention areillustrated. Three rubber compounds were prepared following thecompositions shown in Table 1, with all amounts given in phr and thecompounds further including standard amounts of curatives and additives.The compounds were mixed in a multi-step mix procedure followed bycuring and testing as indicated in Table 2.

TABLE 1 Sample 1 2 Type Control Invention Styrene-Butadiene Rubber ¹, Tg= −20° C. 30 30 Polybutadiene ², Tg = −108° C. 30 30 Natural Rubber, Tg= −64° C. 40 40 Silica³ 70 0 Prehydrophobated Silica⁴ 0 70 Carbon Black1 1 Oil⁵ 1 1 Silane Coupling Agent⁶ 7 0 Resin⁷ 16 16 ¹ Styrene-Butadienerubber solution polymerized, functionalized Tg −20° C. ² Polybutadiene,96 percent cis 1,4; Tg = −108 C., solution polymerized with Nd catalyst,as Budene 1223 from Goodyear. ³Precipitated silica, BET 125 m²/g⁴Prehydrophobated silica as Agilon 400 from PPG ⁵Naphthenic oil⁶bis-triethoxysilylpropyl disulfide, Evonik ⁷Copolymer of styrene andalpha-methylstyrene, Tg = +39° C., obtained as Sylvatraxx4401 fromArizona Chemicals

TABLE 2 Sample Viscoelastic Properties¹ 1 2 G′ (0.83 Hz, 100 C., 15%strain), MPa 0.205 0.231 G′ (1 Hz, 100 C., 1% strain), MPa 1.723 1.295G′ (1 Hz, 100 C., 50% strain), MPa 0.798 0.669 Tan delta (1 Hz, 100 C.,10% strain) 0.100 0.098 Cure Properties² (60 minutes at 150 C.) DeltaTorque, dN-m 16.87 11.94 T25, min 2.3 3.39 T90, min 6.92 11.11 TensileProperties (Cured 10 minutes at 170 C.) 300% Modulus, MPa 10.67 7.18Tensile Strength, MPa 19.83 20.29 Elongation at Break, % 485 610 TearStrength³ (Cured 14 minutes at 160 C.) Strength, N 30.76 103.72 DINAbrasion⁴ (Cured 14 minutes at 160 C.) Relative volume loss 54 80 ZwickRebound⁵ (Cured 14 minutes at 160 C.)  0 C. Rebound 21.5 25.76  23 C.Rebound 41.39 49.19  60 C. Rebound 59.52 64.26 100 C. Rebound 67.31 72.6¹Measured at 2% strain, frequency 0.33/3.33 Hz, 100 C. Data according toRubber Process Analyzer as RPA 2000 instrument by Alpha Technologies,formerly the Flexsys Company and formerly the Monsanto Company.References to an RPA-2000 instrument may be found in the followingpublications: H. A. Palowski, et al, Rubber World, June 1992 and January1997, as well as Rubber & Plastics News, April 26 and May 10, 1993.²Cure properties were determined using a Monsanto oscillating discrheometer (MDR) which was operated at a temperature of 150.degree. C.and at a frequency of 11 hertz. A description of oscillating discrheometers can be found in The Vanderbilt Rubber Handbook edited byRobert 0. Ohm (Norwalk, Conn., R. T. Vanderbilt Company, Inc., 1990),Pages 554 through 557. The use of this cure meter and standardizedvalues read from the curve are specified in ASTM D-2084. A typical curecurve obtained on an oscillating disc rheometer is shown on Page 555 ofthe 1990 edition of The Vanderbilt Rubber Handbook. ³The tear resistanceproperty (tear strength) determination is conducted for peel adhesion ofa sample to another sample of the same material. A description may befound in ASTM D4393 except that a sample width of 2.5 cm is used and aclear Mylar plastic film window of a 5 mm width is inserted between thetwo test samples. It is an interfacial adhesion measurement (pullingforce expressed in N/mm units) between two layers of the same testedcompound which have been co-cured together with the Mylar film windowthere between. The purpose of the Mylar film window is to delimit thewidth of the pealed area. ⁴Data according to DIN 53516 abrasionresistance test procedure using a Zwick drum abrasion unit, model 6102with 2.5 Newtons force. DIN standards are German test standards. The DINabrasion results are reported as relative values to a control rubbercomposition used by the laboratory. ⁵Rebound is a measure of hysteresisof the compound when subject to loading, as measured by ASTM D1054.Generally, the lower the measured rebound at 100° C., the lower therolling resistance.

What is claimed is:
 1. A pneumatic tire comprising a vulcanizable rubbercomposition, the vulcanization rubber composition comprising: 1) 100parts by weight of elastomer consisting of 25 to 35 phr of astyrene-butadiene rubber, 25 to 35 phr of a polybutadiene, and 35 to 45phr of a natural rubber or synthetic polyisoprene, wherein thestyrene-butadiene rubber is a functionalized solution polymerizedstyrene-butadiene elastomer having a glass transition temperature Tg(A)ranging from −30 to −10° C. and having at least one functional group;the natural rubber or synthetic polyisoprene has a Tg(B) ranging from−60 to −70° C.; and the polybutadiene is a cis 1,4 polybutadiene havinga Tg(C) ranging from −110 to −90° C., wherein Tg(A)−Tg(B)≥25° C., andTg(B)−Tg(C)≥25° C.; 2) 60 to 80 phr of a prehydrophobated silica; 3) 1to 10 phr of carbon black; 4) 1 to 3 phr of rubber processing oil; and5) 5 to 25 phr of at least one hydrocarbon resin having a Tg≥20° C.;wherein the weight ratio of hydrocarbon resin to rubber processing oilis greater than
 8. 2. The pneumatic tire of claim 1, wherein thefunctional group comprises at least one of an amino group, a thiol estergroup, an alkoxy group, a hydroxyl group, and a silyl group.
 3. Thepneumatic tire of claim 1, wherein the functional group includes anamino, an alkoxy, and a silyl group.
 4. The pneumatic tire of claim 1wherein the styrene-butadiene rubber comprises functional groupsselected from the group consisting of terminal functional groups, inchain functional groups.
 5. The pneumatic tire of claim 1, wherein theamount hydrocarbon resin ranges from 10 to 20 phr.
 6. The pneumatic tireof claim 1, wherein the amount of carbon black ranges from 1 to 5 phr.7. The pneumatic tire of claim 1, wherein the hydrocarbon resincomprises a copolymer of styrene and alphamethylstyrene.
 8. Thepneumatic tire of claim 1, wherein the weight ratio of hydrocarbon resinto oil is greater than
 12. 9. The pneumatic tire of claim 1, wherein theprehydrophobated silica comprises an alkoxysilane and anorganomercaptoalkoxysilane.
 10. A vulcanizable rubber compositioncomprising: 1) 100 parts by weight of elastomer consisting of 25 to 35phr of a styrene-butadiene rubber, 25 to 35 phr of a polybutadiene, and35 to 45 phr of a natural rubber or synthetic polyisoprene, wherein thestyrene-butadiene rubber is a functionalized solution polymerizedstyrene-butadiene elastomer having a glass transition temperature Tg(A)ranging from −30 to −10° C. and having at least one functional group;the natural rubber or synthetic polyisoprene has a Tg(B) ranging from−60 to −70° C.; and the polybutadiene is a cis 1,4 polybutadiene havinga Tg(C) ranging from −110 to −90° C., wherein Tg(A)−Tg(B)≥25° C., andTg(B)−Tg(C)≥25° C.; 2) 60 to 80 phr of a prehydrophobated silica; 3) 1to 10 phr of carbon black; 4) 1 to 3 phr of rubber processing oil; and5) 5 to 25 phr of at least one hydrocarbon resin having a Tg≥20° C.;wherein the weight ratio of hydrocarbon resin to rubber processing oilis greater than
 8. 11. The vulcanizable rubber composition of claim 10,wherein the functional group comprises at least one of an amino group, athiol ester group, an alkoxy group, a hydroxyl group, and a silyl group.12. The vulcanizable rubber composition of claim 10, wherein thefunctional group includes an amino, an alkoxy, and a silyl group. 13.The vulcanizable rubber composition of claim 10 wherein thestyrene-butadiene rubber comprises functional groups selected from thegroup consisting of terminal functional groups, in chain functionalgroups.
 14. The vulcanizable rubber composition of claim 10, wherein theamount hydrocarbon resin ranges from 10 to 20 phr.
 15. The vulcanizablerubber composition of claim 10, wherein the amount of carbon blackranges from 1 to 5 phr.
 16. The vulcanizable rubber composition of claim10, wherein the hydrocarbon resin comprises a copolymer of styrene andalphamethylstyrene.
 17. The vulcanizable rubber composition of claim 10,wherein the weight ratio of hydrocarbon resin to oil is greater than 12.18. The vulcanizable rubber composition of claim 10, wherein theprehydrophobated silica comprises an alkoxysilane and anorganomercaptoalkoxysilane.
 19. The vulcanizable rubber composition ofclaim 10, in the form of at least one item selected from a tire tread, ashoe, a shoe sole, a vibration isolator, a transmission belt, a hose, aconveyor belt, and a track belt.